STUDIES ON SUITABILITY OF C&D

WASTES IN MANUFACTURING OF
CONCRETE BLOCKS
 INTRODUCTION
The manufacturing of concrete blocks was started during 19 th Century. Over the period of
time these building blocks have undergone enormous transition from solid concrete blocks
to cavity based concrete blocks. Often, concrete blocks are preferred over conventional
burnt clay bricks due to many obvious reasons such as energy efficient building blocks as
compared to bricks as well as saves considerable amount of mortar. Although, Indian
construction industries often use burnt bricks over concrete block due to its ease of
availability. Whereas, literature indicates the coefficient of variation of strength of bricks
may be as high as 35-40%.

Coarse aggregate of size less than 10mm along with fine aggregate is preferred for the
preparation or manufacturing of blocks. Various materials such as Quarry dusty, M-sand etc
are used as fine aggregate in concrete. Apart from these materials, it is necessary to explore
the suitability of other Inorganic Industrial wastes residuals.

India generates considerable amount of construction and demolition wastes. These wastes
are usually dumped in open land which causes ecological issues such as lack of ground water
recharge. This waste material can be effectively utilised as partial replacement to the
aggregates for preparation of mortar and concrete. The percentage replacement of natural
sand by C&D waste can be as high as 40%.

Hence, in the present study an attempt will be made to investigate the suitability of C & D
waste powder (procured from brick masonry wastes) as aggregate in manufacturing of solid
and cavity based concrete blocks. Physical and mechanical properties of the blocks
manufacturing will be ascertained and compared with commercially available blocks of
Bengaluru.

LITERATURE
Suitability of recycled construction and demolition aggregates

Md. Aminur Rahman, Monzur Imteaz - 2013

An attempt has been made to reduce the use of virgin materials and to increase the reuse of
Construction and Demolition (C&D) materials such as Crushed Brick (CB), Recycled Concrete
Aggregate (RCA) and Reclaimed Asphalt Pavement (RAP) as pipe backfilling materials for
storm water and sewer pipes. The recycled materials studied in this research had a
maximum aggregate size of 19 mm. The samples were first oven dried at 60 C until they
were fully dried. Laboratory tests were subsequently undertaken on the above mentioned
recycled materials. Three different types of tests were done i.e. Physical Testing,
Geotechnical Testing and chemical testing. In Physical testing the particle size distribution of
C&D materials was conducted by sieve analysis according to ASTM D422-63. Similarly,
Specific gravity, water absorption, PH, Organic content, Hydraulic conductivity and LA
Abrasion tests were done according to ASTM C127, BS 1377, ASTM D2974 (2007) and ASTM
C131. In Geotechnical testing, Modified compaction test were conducted according to
ASTM-D1557. The large Direct Shear Test (DST) was conducted for the C&D materials at
normal stresses of 30 kPa, 60 kPa and 120 kPa. These values represent the range of stress
that C&D materials will be exposed to in filed application and the tests were conducted as
per ASTM D5321. In chemical testing, PH and other suitability tests were done in
consideration with environmental effects. The results of the laboratory testing undertaken
in this research have shown that RCA and CB satisfied the criteria established by the various
regulatory authorities. On the other hand, some of the specified properties of RAP did not
meet the criteria for its use as a construction material.

Recycled Concrete as Aggregate for Structural Concrete Production

Mirjana Malešev , Vlastimir Radonjanin and Snežana Marinković

A comparative analysis of the experimental results of the properties of fresh and hardened
concrete with different replacement ratios of natural with recycled coarse aggregate is
presented in the paper. Recycled aggregate was made by crushing the waste concrete of
laboratory test cubes and precast concrete columns. They tested concrete with different
propotions of natural and recycled aggregates. It was found that regardless of the mix ratio,
Recycled Aggregate Concrete (RAC) did give satisfactory results.

Grading comparison of NA and RA, Workability was computed via slump test, compression
and flexural strength of both types were determined. Even a beam was cast with RAC and
deflection characteristics with various loads were studied and comparison was made with
conventional beam

Following are the properties of RAC when compared to Natural aggregate concrete. (NAC):

- increased drying shrinkage up to 50%

- increased creep up to 50%
- water absorption increased up to 50%
- decreased compressive strength up to 25%
- decreased splitting and flexural tensile strength up to 10%,

- decreased modulus of elasticity up to 45%, - same or decreased frost resistance.

According to the test results, the performance of recycled aggregate concrete, even with
the total replacement of coarse natural with coarse recycled aggregate, is mainly
satisfactory, not only in terms of the mechanical properties, but also the other requirements
related to mixture proportion design and production of this concrete type. The only two
properties those are lower than for the natural aggregate concrete properties are the
modulus of elasticity and shrinkage deformation. Because of that, it is not recommended to
apply this type of concrete for structural elements for which large deformations can be
expected. Also, this type of concrete shouldn’t be used for structures exposed to aggressive
environment conditions without appropriate previous testing. Deflections of tested beams
do not depend on the type and quantity of used aggregate in the elastic area—similar
deflections were registered regardless of the concrete type. Grading comparison of NA and
RA, Workability was computed via slump test, compression and flexural strength of both
types were determined. Even a beam was cast with RAC and deflection characteristics with
various loads were studied and comparison was made with conventional beam.

Experimental Study on Special Concrete by Replacement of Aggregates with ‘Quarry Dust’

and ‘Broken Glass’

J.Gopi Krishna , J.R.Thirumai

In the laboratory quarry dust has been tried as fine aggregate in place of sand and broken
glass has been used as partial substitute to conventional coarse aggregate in concrete
making. Cubes, cylinders and prisms were cast and tested for compressive strength, split
tensile strength and flexural strength after a curing period of 28 days. The basic tests on
quarry dust were conducted as per IS-383-1987 and its specific gravity was around 1.95.
Wet sieving of quarry dust through a 90 micron sieve was found to be 78% and the
corresponding bulking value of quarry dust was 34.13%. Crushed granite coarse aggregate
conforming to IS 383-1987 of size 20 mm and down having a specific gravity of 2.6 was used.
A clean dry glass powder is useful as a substitute for Portland cement in concrete. The finely
ground glass having a particle size finer than 38 micro meter contain a high amount of
amorphous silica, which exhibits a pozzolanic behavior. Hence, the use of ground glass in
concrete can be advantageous with respect to hardened properties and durability.
Moreover, using waste glass as fine aggregate would produce better workability in concrete,
provided its geometry is almost spherical and preferable to produce a workable mixture.

The compressive strength and split tensile strength of concrete containing broken glass
aggregate is retained more or less in comparison with controlled concrete specimens.
However strength noticeably decreased when the broken glass content was more than 15%.

Thus we can say that use of glass as a replacement is will lead to reduction in strength to a
certain extent.

Experimental study on the properties of concrete made with alternate construction materials

Prof. R. Sathish Kumar Sr. Associate Professor National Institute of Construction

Management and Research, Hyderabad

In this paper, Experimental studies were carried out to find the suitability of the alternate
construction materials such as, rice husk ash, sawdust, recycled aggregate and brickbats as a
partial replacement for cement and conventional aggregates. For this concrete cubes of size
150mm x150mm were casted with various alternate construction materials in different mix
proportion and with different water cement ratios. Their density, workability and
compressive strengths were determined and a comparative analysis was done in terms of
their physical properties and also cost savings. The results showed that the compressive
strength, of recycled aggregate are on average 70% to 80% of the natural aggregate
concrete and the compressive strength of brick bat concrete and saw dust concrete was
found to be in the range of 30-35% and 8-10% respectively. The compressive strength of rice
husk ash concrete was found to be in the range of 70-80% of conventional concrete for a
replacement of cement up to 20%.

The compressive strength of concrete cubes were determined with different proportions
and water/cement ratio and the following inferences were made:

 They found that compressive strength of rice husk ash concrete was in the range of
70-80% of conventional concrete for a replacement of cement up to 20%.
 They also concluded that the early strength of rice husk ash concrete was found to
be less and the strength increased with age.
 The rice husk ash concrete occupies more volume than cement for the same weight.
So the total volume of the rice husk ash concrete increases for a particular weight as
compared to conventional concrete which results in economy.
 Due to the lower density of RHA concrete the self weight of structure gets reduced
which results in overall savings.

 Recycled aggregate posses relatively lower bulk density, crushing and impact values
and higher water absorption as compared to natural aggregate.
 The compressive strength of recycled aggregate concrete was found to be in the
range of 70 to 80 % of conventional concrete..
 The compressive strength of brick bat concrete was found to be nearly 35 % of
conventional concrete... The compressive strength of saw dust concrete was found
to be nearly 10 to 15% of conventional concrete. So the concrete made with
alternate construction materials like brick bats and saw dust can be used for
partition & filling purposes & nailing purposes where the strength is not the criteria.
 Wherever compressive strength is not a criteria, the concrete made with alternate
construction materials can always be preferred.

Rice husk ash (RHA) is obtained by the combustion of rice husk. The burning temperature
must be within the range of 6000C to 8000C. The ash obtained has to be grounded in a ball
mill for 30 minutes. Here it must be noted that production of rice husk ash involves a lot of
energy consumption. Hence there is a scope for other materials to be used like C&D waste.
The results for brick bat concrete are not satisfactory, but there is further scope for studies
on flexure characteristics by preparing actual blocks and doing more tests for flexural
strength.

An Experimental Study on Partial Replacement of Sand with Crushed Brick in Concrete

M.Usha rani, J. Martina Jenifer-Department of civil engineering ,R.M.K. Engineering College,

Chennai
Objectives of the study were to evaluate the utility of crushed brick as a partial replacement
of sand in concrete, To study and compare the performance conventional concrete. To
understand the effectiveness of brick as in strength enhancement. Brick bats crushed in
coarse powder form were used as a fine aggregate for making concrete. The waste bricks as
obtained from garbage of a broken building were collected and pulverized to get the particle
passing 4.75 mm sieve and retained on 0.075 mm sieve to get the grading of fine aggregate.
15, 20 and 25% brick powder is used as replacement of sand in the experiments. In order to
study the effect of replacement of sand in various ratio of crushed brick 36 numbers of
cube of 150mm size, 36 numbers of beams of size 100 mm x 100 mm x 500 mm and 36
numbers of cylinders of 150mm diameter to a height of 300mm were cast and used as test
specimens to determine the compressive strength, flexural strength and split tensile
strength respectively at the age of 7,14 and 28 days. The samples with 15% and 20%
concrete were found to gain more early strength(17.62% and 19.82% more) when
compared to the mix with no replacement and the 28 day strength of those were 7% and
9.12% more, but 25% replacement caused decrease in strength (27.89% less for 28 day
strength) . Similar results were obtained in flexure and split tensile strength. Thus it was
concluded that 20% replacement has more advantages than concrete with no replacement.

Study of Properties of Concrete with Partial Replacement of Coarse Aggregate by Ceramic

Waste and Fine Aggregate by Stone Dust
Juned Ahmad, Meraj Ahmad Khan, Abdullah Anwar
This study was conducted to analyze the compressive and flexural strength of concrete
when natural sand was replaced with stone dust at 20%, 40 %, 60%, 80 % and 100% along
with 20 % replacement of coarse aggregate by ceramic waste. To increase the workability of
concrete Superplast was used as a super plasticizer. The percentage of ceramic waste is kept
20% for all specimens. It is found that at 40 % replacements of natural sand with stone dust
along with 20% replacement of stone aggregate by ceramic waste, the compressive strength
as well as flexural strength reached their maximum values, as compared to other
proportions. It is also found that it is not feasible using ceramic waste alone as a
replacement of coarse aggregate because it decreases the compressive as well as flexural
strength of concrete considerably. The study concludes that the stone dust with 20 % of
ceramic waste as a coarse aggregate can be employed effectively as a choice of natural sand
for nominal concreting up to 40 % for M20 grade of concrete.

The ceramic waste used as the substitute for coarse aggregate. They have been crushed
manually into the required size of 20 mm approximately. The impact value was found to be
22.53%. The Stone Dust used as the substitute of natural river sand is of specific gravity 2.5
and the size of it is less than 4.75 mm. The grade of concrete, which we adopted, is M20
with the water cement ratio of 0.48. The compressive and flexural strength of concrete with
40% replacement of natural sand by stone dust along with 20% replacement of coarse
aggregate by ceramic waste reveals higher strength as compared to 0 % replacement of
natural sand by stone dust along with 20% replacement of coarse aggregate by ceramic
waste. It is found that as compared to flexural strength the compressive strength greatly
decreased when only ceramic waste is used as a 20% replacement of coarse aggregate
(i.e.at 0% stone dust and 20 % ceramic waste).
So it is advised on the basis of the present study that ceramic waste alone could not be used
as a replacement of coarse aggregate because it adversely affect on the properties of
concrete. On the other hand, if it is used with the stone dust it gives satisfactory results on
40 % of replacement of fine aggregate with stone dust. The properties of concrete are found
to be enhanced upto 40 % replacement of fine aggregate with stone dust and after that it
decreases. Thus we found out the optimum percentage for replacement of stone dust with
fine aggregate along with 20% replacement of coarse aggregate by ceramic waste is almost
40%. Here the procurement of replacement materials might be an issue as the stone quarry
and ceramic manufacturing units might not be available at an economical transportation
cost, whereas construction and demolition waste can be obtained locally.

OBJECTIVES
METHODOLOGY
Cement

Cement should comply with SANS 50197-1. Strength class should be 42,5N or higher
because the concrete must develop strength as rapidly as possible.

Aggregates

Sand and stone are used for most block production. Sand and stone are fragments of rock
and differ only in size. Sand particles will pass through a sieve with 4,75 mm square
openings. Stone particles will not. All aggregates should be clean and not contain organic
matter such as roots or humus. If the aggregates contain clay it should be in a very small
fraction.

The following aggregates may be considered:

• Fine sand with particles mainly smaller than 1-mm: pit, fine river or dune sand

• Coarse sand with the biggest particles approximately 5-mm in size: crusher, pit or coarse
river sand

• Stone with a maximum size of 13-mm for bricks or solid blocks or 10-mm for hollow blocks
It is normally possible to make blocks with coarse sand on its own.

Alternatively combinations of aggregates may be used:

• A blend of coarse sand and fine sand

• A blend of fine sand and stone

• A blend of fine sand, coarse sand and stone. For small-scale production, the best
aggregate or combination of aggregates is normally found by trial and error.

Water

Water that is fit for drinking is suitable. Most river and borehole water may be used.

Trial Mixes

The aim is to find a mix that will produce blocks that have an acceptable texture and are
strong enough but as cheap as possible. Because cement is more expensive than aggregates,
the lower the cement content the cheaper the block. Strength of well cured blocks depends
on:

• Aggregate: cement ratio

• Degree of compaction

• Size of block, solid or hollow.

The degree of compaction depends on:

• Overall grading of the aggregates

• Particle shape of aggregates

• Aggregate: cement ratio

• Water content

• Compactive effort

It can be seen that strength depends on a number of interrelated factors. It is therefore not
possible to design a mix in a laboratory. Instead, a trial-and-error process, using the
equipment of the block yard, is followed. This process aims to arrive at the best combination
of aggregates and the right aggregate: cement ratio.

Aggregates

First try coarse sand only. Then try replacing some of this by fine sand and some by stone, if these
materials are available. Alternatively, if coarse sand is not available, try different blends of fine sand
and stone.

Aggregate:cement ratio

Try 6:1, 8:1 and 10:1 by loose volumes (230, 300 and 380-l of aggregate respectively per 50-kg bag of
cement).

Batching
Cement, if supplied in bags, should preferably be batched by the full bag. Cement supplied in bulk
may be weighed (preferable) or batched by loose volume. It is important to batch all materials
accurately. Batching containers, eg wheelbarrows, buckets, drums and wooden boxes, should be
loosely filled to the brim and struck off flush with it. To avoid errors, there should be enough
containers for a full batch to be made without using any container more than once. Dented or
broken containers must not be used. The amount of water to be added to the mix is judged by eye
and by doing some simple tests (see Water content below). Time can be saved if, once the
approximate quantity of water per batch is known, about 90-% of this is measured out and added to
the mix at the start of mixing. The rest of the water can then be judged by eye and by test. Water
content Water content is critical. The mixture must be wet enough to bind together when
compacted, but it should not be so wet that the blocks slump (sag) when the mould is removed. A
common mistake is the use of mixes that are too dry, resulting in incomplete compaction. The
moisture content should be as high as possible as this allows better compaction and thus gives the
best strength. Moisture content is approximately right when ripple marks form on a steel rod or the
back of a shovel when it is rubbed against some of the mixture. The water content is just over
optimum when ripple marks start appearing on blocks when they are demoulded.

Mixing

Hand mixing should be done, using shovels, on a level concrete slab or steel plate. First spread the
aggregate out 50 to 100-mm thick. Then distribute the cement, and stone if any, evenly over the
sand. Mix aggregate and cement until the colour is uniform. Spread the mixture out, sprinkle water
over the surface and mix. Continue with this process until the right amount of water has been mixed
in. For machine mixing, first mix aggregate and cement then add water gradually while mixing until
water content is correct.

Moulding

Hand operated machines should be used as instructed by the manufacturer. The mould of a
powered machine should be filled until approximately six to eight cycles of compaction are required
to bring the compacting head to its stops. Too little or poor compaction should be avoided as it
results in greatly reduced strengths. Demoulding or removal of the mould should be done carefully
so that the fresh blocks are not damaged. Fresh blocks should be protected from rain with plastic
sheets or any suitable covering during the first day and from the drying effects of the sun and wind
until curing starts.

Curing

The day after production, blocks should be removed from the production slab or pallets and stored
in the stacking area, ready for curing. Stacks should be carefully built to avoid chipping edges and
corners. Curing is the process of maintaining satisfactory moisture content and a favourable
temperature in the blocks to ensure hydration of the cement and development of optimum
strength. In the South African climate it is normally sufficient to cover blocks with plastic sheeting to
prevent moisture loss or to spray blocks with water. Blocks should be cured for at least seven days.
Strength
Quality of blocks should be controlled so that strengths are adequate (to avoid breakages or
rejection by customers) and mixes are as economical as possible. Ideally, blocks should be regularly
tested for strength and mixes and production processes modified if necessary. If testing is
impracticable or unaffordable, block strength should be continually assessed by noting whether
corners and edges, or even whole blocks, tend to break in handling. Strength can also be assessed by
knocking two mature bricks together.

Dimensions

The length and width of the units are determined by the mould and will not vary greatly. However,
the height can vary and should be monitored using a simple gauge. Units of inconsistent height will
lead to difficulties in the construction of masonry and possible rain penetration.

Shrinkage

Concrete masonry units shrink slightly after manufacture. In order to avoid this happening in the
wall, blocks should be allowed to dry out for at least seven days before being used for construction.